The following meanings for the abbreviations used in this specification apply:    ATB Adaptive Transmission Bandwidth    BSR Buffer Status Report    CA Carrier aggregation    CC Component carrier    CoMP Coordinated Multi Point    CQI Channel quality indicator    CRC Cyclic Redundancy Check    DL Downlink    DC Dual carrier    DCI Downlink control information    DL Downlink    eNB enhanced Node-B    E-UTRA Evolved Universal Terrestrial Radio Access    HetNet Heterogeneous networks    HO Handover    HSDPA High speed downlink packet access    L1 Layer 1    L2 Layer 2    LTE Long term evolution    LTE-A LTE-Advanced    MAC Media access control    MUX Multiplex    PCell Primary Cell    PDCCH Physical downlink control channel    PDU Packet data unit    PHR Power headroom report    PUCCH Physical uplink control channel    PUSCH Physical uplink shared channel    RRM Radio resource management    SCell Secondary Cell    TA Timing advance    TAG Timing advance group    UCI Uplink control information    UE User equipment    UL Uplink    U-plane User plane    WCDMA Wideband code division multiple access
Embodiments of the present invention relate to LTE carrier aggregation (CA)/CoMP. In particular, Rel-10 of the E-UTRA specifications introduces carrier aggregation (CA), where two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. In CA it is possible to configure a UE to aggregate a different number of CCs originating from the same eNB and possibly different bandwidths in the uplink (UL) and downlink (DL). In addition, configured CCs can be de-activated in order to reduce the UE power consumption: the UE monitoring activity of a de-activated carrier is reduced (e.g. no PDCCH monitoring and CQI measurements). This mechanism is referred to as carrier activation/de-activation.
The deployment of low-power eNBs in areas with already existing macro cell coverage yields cellular systems with overlapping layers of macro cells and smaller cells (e.g. pico cells). These types of network deployments are also known as heterogeneous networks (HetNet). In the latest years heterogeneous networks have become topic of research activities and extensive work in standardization bodies. One of the most critical and challenging tasks in heterogeneous networks is efficient support of mobility. Moreover, traffic steering between different network layers also becomes an important task for operators.
Recently, also inter-site CA has been proposed. Inter-site CA means that a primary cell (PCell) and a secondary cell (SCell) are transmitted to/received from non-co-sited access nodes. That is, when applying inter-site CA, a UE is connected to multiple non-collocated eNBs via separate frequency carriers or same frequency. One eNB is controlling a primary cell (PCell) or primary component carrier, and possibly one or more secondary cells (SCell) or secondary component carrier, while the other eNB is controlling one or more SCells or secondary component carriers.
An example is shown in FIG. 1, in which a UE is connected to a macro-eNB (a first eNB) and to a pico-eNB (a second eNB). The macro-eNB is using carrier F1 (PCell or primary component carrier), whereas the pico eNB is using carrier F2 (SCell or secondary component carrier). Between the two eNBs, an interface is provided, which is usually an X2 interface, and only if the pico eNB should be a Home eNB, then this is defined as S1. That is, between the eNBs there is a link (also referred to as backhaul link) via X2 interface or other. Such a link is characterized by high latency and/or high jitter, which poses a problem for the above-described inter-site CA.
For scheduling uplink transmission, uplink (UL) scheduling information e.g. Buffer Status Report (BSR) and Power Headroom Report (PHR) has to be reported from the UE to the eNB to assist the UL scheduling at the eNB.
However, currently no specific way of supplying such UL scheduling information from the UE to several eNBs is provided and should be specified in case of inter-site UL CA with X2 interface (or similar high latency backhaul link) between the nodes.